The invention is directed to an NMR head imaging system using permanent magnets to establish the uniform imaging field.
The related application, whose full contents are herein incorporated by reference, describes a magnetic structure designed for NMR head imaging in interventional procedures. The requirements to be satisfied are described in detail in the related application. These requirements are satisfied by a permanent magnetic structure capable of generating a uniform field for NMR imaging over a region of interest encompassing the head of a patient and that is open at one side allowing access to the head of the patient by a physician for surgical or other medical purposes. In a preferred embodiment described in that application, the magnetic structure of the invention comprises a head structure generating a uniform magnetic field in a region of interest encompassing the patient""s head, coaxially aligned with a shoulder structure generating a magnetic field that extends the uniform field to a second larger region encompassing the patient""s shoulder, and joined to the head structure by a coaxially aligned transition structure which maintains the uniform magnetic field in the region connecting the first and second regions. A feature of that invention is a magnetic structure comprising a single pole piece that extends throughout the structure, which pole piece is connected to the head, shoulder, and transition magnetic structures, with the single pole piece in the shoulder region being configured to house a second magnet that cooperates in extending the uniform field to the shoulder region.
An object of the present invention is an improved NMR head imaging system that can be open from three sides thereby improving access by the operating surgeon, while at the same time provides a maximum strength of the NMR imaging field.
These objects are achieved in accordance with one aspect of the invention by a structure of the magnet characterized by a conical section connected to a larger cylindrical section, wherein the region of interest in which the uniform field is centered along the cone axis.
The region inside the larger cylindrical magnet is configured to accommodate the patient""s shoulders.
In a preferred embodiment, the region inside the conical magnet is constituted of a high-permability ferromagnetic material defined below.
In a further preferred embodiment, the magnetic structure comprises opposed, spaced circular-symmetric structures with the region of interest falling within a cavity between the circular-symmetric structures. In still another preferred embodiment, a second larger cylindrical magnet extends over the each of the circular-symmetric structures.
The three main permanent magnetic components of the structure of the preferred embodiment are all magnetized in the same direction, preferably parallel to the axis of the conical segment.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described the preferred embodiments of the invention, like reference numerals or letters signifying the same or similar components.